Illumination-measuring device



W. HARRISON.

ILLUMINATION MEASURING DEVICE.

APPLICATION FILED NOV. I3, I9I8.

Patented Feb. 17,1920.

2 SHEETS-SHEET l Invient'or': Ward H arr-'son by l L His Attorney.

W. HARRISON. |LLUM|NAT0N MEASURING DEVICE. APPLICATION 'FILED NOV. I3.1918.

1,331,062. f Patented Feb. 17,1920.

' ZSHEETS-SHEET 2.

' rfiglofm35 e. rw.

Inventor-1 \X/arcl Har-vison,

by WZL@ His Attorney.

Cleveland, county WARD HARRISON, OF CLEVELAND, OHIO, ASSIGNOR TO GENERALELECTRIC COMPANY,

A CORPORATION OF NEW YORK.

ILLUMIN ATION-MEAS'U-RIN G DEVICE.

Appiication fud November 13, 1918.

To all whom t may concern.'

Be it known that I, VARD HARRISON, a citizen of the United States,residing at of Cuyahoga, State of Ohio, have invented certain new anduseful Improvements in Illumination-Measuring Devices, of which thefollowing is a specification.

My invention relates to illumination measuring devices and moreparticularly to devices for measuring the efficiency of light reflectingand transmitting media. The oblject of my invention is to provide adevice by means of which such efficiency may be quickly and convenientlymeasured and which will therefore be useful in maintaining a, higherstandard of quality for reflectors, diffusers and other devicescomprising reflecting and transmitting surfaces.

struments.

In the efficiency measuring device of my invention, I provide a chamberfor the multiple reflection of the light transmitted or reflected bymedia of such characteristics from a light source. Leading from thereflection chamber, I provide a passage-way to an indicating member.Above the indieating member, I provide taining any suitable means forgiving a graded intensity of illumination on the upper surface of theindicating member from a second light medium whose efficiency is to bemeasured placed so as to cover the reflection chamber and in the case ofa reflecting medium, the first light source is placed between the mediumand the chamber but in the case of atransmitting medium, thetransmitting medium is placed between the first light source and thereflection chamber. I prefer to place the two light sources in series inorder to eliminate electrical measuring in- Heretofore, for instance,Whenever it has been desired to find the reflection factor of areflector, it has been necessary to secure the distribution curve of thebare lamp for which the reflector was designed and also the distributioncurve of the reflector with the lamp, which requires a total of thirtyor more readings. After these two distribution curves have beensecuredhconsiderable time has been spent in mathematical calculationbefore the final result, the valueY of the reflection factor, has beenobtained.

While it isppossible to secure al standard Specification of LettersPatent. l

a housing consource in the housing. The` Patented Feb. 17, 1920. SerialNo. 262,292.

distribution curve for a standard incandescent lamp, the distributioncurve of the re- Hector and lamp must be secured for each reflectorbecause reflecting surfaces of reflectors of identical contour may varybetween wide limits. In securing a distribution curve, a certain amountof skill and considerable time are required. On lordinary inspection,the reflecting surfaces of two reflectors may appear no different inquality, but the results of photometric tests may show ay difference ofl0 0120 per cent. in their reflection factors. It is, of course,impractical for the reflector manufacturers to check their products byobtaining distribution curves for each lot of reflectors which theysell, for the time and expense involved would be prohibitive. With myinvention, it is possible to determine the reflection factor of areflector directly in percentage in one reading witliin approximately 2per cent. No special skill is required upon the part of the operator.Another incidental advantage possessed by the preferred form of myinvention is that the use of voltmeters or other instruments 'isdispensed with. This arises from the fact that the two lamps whichconstitute the light sources in my device are operated in series andhence variations in current or voltage in the circuit affect both lampsto the same eXtent and any difference in illumination on one side of theindicating member is balanced by acorresponding difference on the otherside.

In the accompanying drawings, Figure 1 is an elevation view of one formof my invention;

Fig. 2 is a top plan view ofthe same;

Fig. 3 is a sectional eleva-tion on the section line A-A of Fig. 2;

Fig. 4 is a partial sectional elevation on :1n-enlarged scale on thesection line B-B of Fig. 2;

Fig. 5 is a bottom plan view of the -reflecting louver;

Fig. 6 is an enlarged sectional elevation showing the indicating memberand adjacent parts;

Fig. 7 is a top plan view of the indicating member; y

Fig. 8 isa top plan view of another form of my invention; "M

Fig. 9 is a sectional elevation on the section line C*C of Fig. 8;

Fig. l0 is a top plan view of a form of ter of Paris shield 5 myinvention used for determining the efficiency vof transmitting surfaces;

Fig. 11 is a sectional elevation on the section line D-D of Fig. 10.

Referring now to Figs. 1, 2 and 3, it will be seen that in thisillustrated form, my invention consists of a container 1 filled withplaster of Paris 2 which has been formed into -a concave basin 3 in thecenter of which a lamp 4 is supported by a plaster of Paris standard 5so located that when a reflector 6 (shown in Fig. 3 only) is placed overthe basin 3 the light source will be in the same position with respectto the reflector 6 as is a lamp when the reflector is in ordinary use.The lamp 4 is partly surrounded by a plasforming the upper end of thesupporting standard 5. The shield 5 cuts 0H all direct light from thelamp 4 which would otherwise fall on the reflecting surface of thebasinv 3, but permits direct rays to reach every point on the innersurface of the reflector 6. A passage 7 leads from the basin 3 up to theindicating member 8 which is covered by the housing 9 to which isatt-ached a lamp box 10 and a sighting passage 11 open at the upper endand slanted so that the eye may see the indicating member 8.

eferring'now to housing 9 contains a a rod 13, one end of the housing 9above Figs. 4, 5, 6 and 7, the louver 12 mounted upon which passesthrough the lamp box 10 and the other, nearthe bottom of the oppositedside. The lower end of the rod 13 is fastened to a knurled disk 14 whichis used to rotate the louver 12. The portion of the rod 13 between thedisk 14 and the louver 12 is threaded and fitted with a wing nut 15 andsuitable washers 16. A wedgeshaped portion 17 of the surface of thelouver 12 is white, the remainder 18 being black. The louver 12 ischamfered at the corners in order to permit it to be rotated about therod 13 in the housing 9.

The aperture 20 between the)l housing 9 and the lamp box 10 is so madeand placed with respect to the lamp 19 that direct light from thissource falls upon the louver 12 at a point at least as high as the apexof the wedgesh-aped white portion 17 but not upon the indicating member8. The indicating member 8, which is not per se my invention but hasbeen used heretofore, consists of a rectangular piece of clear glass 21on the upper surface of which is placed a similar iece of thintranslucent paper 22 covered y a similar piece of opaque paper 23pierced at regular and frequent intervals along its center andthroughout its length by small round holes 24. A scale 25 is laid out onthe opaque paper 23 parallel to the holes 24. s

When a reflector 6 is placed over the basin 3, the light from the lamp 4first strikes the lbe locked in position by flection factors varyreflecting surface and is directed down to the surface of the basin andback again many times. A portion of the light, however, finds its waythrough the passage 7 to the under side of the indicating member 8 an'dilluminates it uniformly to yan intensity which is dependent on theamount of light directed downward by the reflector. The upper side ofthe `indicating member. 8 is illuminated to a graded intensity by thelight. directed downward bv the wedgeshaped white. portion 17 of thelouver 12 from the lamp 19. At the point on the opaque paper 23 wherethe value of the graded intensity equals the value of the illuminationin the passage 7, the hole 24 will seem to disappear. On either side ofthis hole 24, the other holes will appear brighter or darkerrespectively. The reading on the Scale 25 corresponding to the hole 24is an indication of the reflection factor of the reflector 6. Byrotating the louver 12 by means of the nurled disk 14, the disappearinghole, that is, the point of balanced illumination, may be brought to anyposition along the scale 25. lThe louver 12 may then tightening the wingnut 15.

The simplest use ofi my device is to determinel whether one reflector ofunknown i the reference point, the reflection factor of the secondreflector is the same as -that of the standard. If the scale reading ishigher or lower than the reference point, it is an indication that thereflection factor is respectively higher or lower."

However, the scale 25 may be calibrated to give the reflection factorsdirectly in per cent. For this work it is necessary to use at least twostandard reflectors whose reover a considerable range. By takingreadings on the scale 25 for each reflector and plotting these readingsagainst the4 respective known reflection factors in per cent., thereflection factor of an unknown reflector may be determined by takincg ascale reading and finding the correspon ing reflection factor in percent. fron the curve. The indicating device may ther be removed and thescale of corresponding reflection factors in per cent. be superim posedupon the scale 25. Then any reflecto; may be placed over thebasin 3 andits re flection factor in per cent. lmay be read di rectly from thesuperimposed scale. For such measurements, my device is accurate towithin about 2 per cent. and this accuracy is due to the multiplereflections within the device which tend to magnify (or raise to -ahigher power) any difference in the reflection factors.

Although in the preceding description of my invention I have said thatthe basin 3 and supporting standard 5 were made of plaster of Paris,they may be made of metal or other material finished in white or asimilarly good reflecting surface. Although, in the housing 9 I haveused a louver l2 with a white wedge-shaped portion 17 and a dark portion18, any device which will give a graded intensity of illumination uponthe upper surface of the indicating member 8 may be used.

In Figs. 8 and 9 is shown another form of -my invention which may beused to determine the reflection factor of flat surfaces. The container26 has Aa shallow dome 27 corresponding' to the basin 3 of Fig. 3. Thesupporting standard 28 with lamp shield 29 carries a lamp 30. Apassage-way 3l leads from the dome 27 to the indicating member 32. Thehousing 33 contains a louver (not shown) to secure a graded intensity onthe upper side of indicating member 32 and has attached to it thesighting passage 34 and lamp lbox 35 containing the lamp 36 electricallyconnected in series with the lamp 30. In operation the indicating member32 is calibrated through the use of at least two flat reflectingsurfaces placed under the dome 27.

In Figs. l0 and ill, I have shown ya form of my invention which may beused for determining the efficiencyof a transmitting medium. Thecontainer 37 has a shallow basin 38 with a passage 39 leading to theindicating member 40. The housing 4l corresponds with the housing 9 ofFig. 3 and contains a louver (not shown) to secure a graded intensity onthe upper side of the indicating member 40 from the lamp 42 contained inthe lamp box 43 attached to the housing 4l. A sighting passage 44 isalso provided. Over the basin 38 is placed a lamp box 45 with a lamp 46electrically connected in series with the lamp 42. The inner surface ofthe lamp box 45 is painted black. The transmitting medium 47 is placedbetween the lamp boX 45 and the basin 38. In operation, the indicatingmember 40 is cali- Ibrated through the use of at least two transmittingmedia placed between the lamp box 45 and the basin 38. 4

lVhat I claim as new and desire4 to secure by Letters Patent of theUnited States, is,-

l. A device for measuring the elliciency of a light reflecting ortransmitting medium comprising a light source mounted to illuminatesaidmedium, a reflecting means medium and means disposed opposite to saidmedium and forming therewith a chamber, an indicating medium, a passagecommunicating with said chamber and leading to said indicating forcomparing the illumination cast upon said indicating medium with that ofa standard.

2. A device for measuring reflecting elliciency comprising a support fora reflecting medium, a reflecting means disposed opposite. thereto andforming a chamber therewith, a light source in said chamber, anindicating medium, a passage communicating with said chamber and leadingto said indicating medium the illumination cast upon said indicatingmedium with that of a standard.

3. A device for measuring the efficiency of a light transmitting orreflecting medium comprising a light source disposed so as to illuminatesaid medium, a chamber provided with means for producing an evenintensity of illumination therein disposed so as to receive illuminationfrom said medium, an indicating` medium mounted to receive illuminationfrom said chamber and means for comparing said illumination with that ofa standard.

4. A device for measuring the efhciency of a light transmitting orreflecting medium comprising a light source disposed so as to illuminatesaid medium, a reflecting means disposed relative to said mediumso as toform therewith a chamber in which the illumination from said medium isreflected repeatedly back and forth to produce an even illuminationtherein, an indicating medium mounted to receive illumination from saidchamber and means for comparing said illumination with that of astandard.

5. A device for measuring the efficiency of a light transmitting orreflecting medium comprising a light source disposed so as to illuminatesaid medium, a chamber provided with means for producing an evenintensity of illumination therein disposed so as toV receiveillumination from said medium, an indicating device comprising a seriesof alternate opaque and translucent portions mounted to receiveillumination on one side thereof from said chamber, a second lightsource disposed on the opposite side of said indicating device and meansfor reflecting light of a graded intensity from said second source uponsaid indicating device.

6. A device for measuring the efficiency of a light transmitting orreflecting medium comprising a light source disposed so as to illuminatesaid medium, reflecting means disposed relative to said medium so as toform therewith a chamber in which the illumination fr`om saidmedium isreflected repeatedly back and forth to produce an and means forcomparingl even illumination therein, an indicating device comprising aseries of alternate opaque and translucent portions mounted to receiveillumination on one side thereof from said chamber, a second lightsource disposed on the opposite side of said indicating device and meansfor reflecting light of a graded intensity from said second source uponsaid indicating device.

's'. A device for measuring the eiiiciency of a light reflecting ortransmitting medium comprising a light source mounted to illuminate saidmedium, reecting means disposed opposite to said reflector and formingtherewith a chamber, an indicating device, a passage communicating withsaid chamber and leading to said indicating device comprising alternateopaque and translucent areas, a second light source disposed on the sideof said indicating device opposite from said passage and means fordirecting light from said second source of a graded intensity upon saidindi 'ating device.

8. A device for measuringreflecting eiliciency comprising a support fora reflecting medium, a reiiecting means disposed opposite thereto andforming a chamber therewith, a light source in said chamber, anindicating device, a passage communicating with said chamber and leadingto said indicating device comprising alternate opaque and translucentareas, a second light source disposed on the side of s aid indicatingdevice opposite to said passage and means Jfor directing light from saidsecond source of a graded intensity upon said indicating device.

In witness whereof, I have hereunto set my hand this eighth day ofNovember, 1918.

WARD HARRISON.

